Phase discriminators



NOV. 4, 1958 v R.. M, DUNHAM v 2,859,347

PHASE DISCRIMINATORS Y Original Filed 001'.. 16, 1952 PHASEDISCRIL'IINATDRS n'Ricl1ard"'M. Duham,"Wayland,`Mass., assignor to Ray-"theon'Manufactui'ing Company, Newton, Mass., a cor- -poration ofDelaware 91Glaims. (61.'1250-36) .is a-continuationfofmy application,Serial No'. 315,148, Iiiled-ctober -16, 195.2; now abandoned.

'i'his :invention Arelates to phase idiscriminator ciruits, .and -moreparticularly to such fa circuit yused to control the frequency of avoltage-sensitivel oscillator by :means .ofa regulating voltagedepending #upon Vthe phase differ- .encc lhetweenthe leadingedges 'ofthetpulse to be regu- .latedand the synchronizing pulse.

Itis `frequently necessary to control-the frequency of an oscillator-with reference to synchronizing `pulses. 4Certain types of oscillators,.-such .as Y-an fastable `plate-to- ,grid lcoupled multivibraton :may beycontrolled in frequency'bythevoltageapplied vto them. 'inthe presentxinvention, such a vvoltage is made-dependent upon the .phase differencebetween the -wave :forms of the :controlledoscillations andthesynchronizing pulses. This voltageis obtained byclamping thesynchronizing pulses to the -wave form to be regulated, and .applying-the clamped `pulsesto the lgridof a second :cathode follower normallybiased to cutol which hasta grid-controlled .tube as .its loadimpedance. This 1grid-controlled tube ,is.normally Abiased to cutoff andthefsynchronizing pulses -applied to its grid. The voltage appearingacross .the Aplate-to-cathode circuit of the output tube Ais `a ,-pulsevarying lin .amplitude with--the udifference in fphase betweenthesynchronizing pulse :and the wave Vform of the output of thecontrolled oscillator. This .pulse -is inte- .grated in a capacitor andYapplied -through a cathode follower to the Vcontrolled oscillator tomaintain 4its frequency at the desired value.

`Other and further advantages '-of this invention will Jbe apparent as`the description thereof progresses, reference-being had to `thelaccompanying drawings wherein:

Fig. 1 -s a schematic diagram of .anfemb'odiment of the invention;

Pig. 2a Ais ra voltage-time 4graph of the waveform-bf the .output -ofrthe oscillator .to be controlled;

16 is 1 connected between -theplate -A117 and rthefcathode `15 oftubey1f?) Ythrough a loady resistor'1'8. :Thescathode 15 ofthe tube 13 'isconnected tothe'ca'thode'120 ofa diode A21, the plate 22 of which=isconnectedto'thef-grid second cathode lfollower 24 isconnectedtoafsouee'of 33 of a third cathodefollo'wer 34'through a rs'istor'35 yshunted 'by a `rectifier vr36. A source "37iof synchronizing l .pulsesisfcoupledthrough4 a capacitor 38, andar` resistor t0-to the Vgrid 41ofthe tube 32. yfA Vcapacitor 14N-iis connected Vbetween `the ,grid 33and cathode'iS of the third lcathode follower 34 through 'aresistor'vfG. he

-output o'f -the `third cathode `follower-"34, taken f from across theYload "resistor 4,6, `is 'conectedfto fahc'oitrol pointon the4controlled oscillator 10 overf-coniuctorw. This control vpoint`v`depends,` of'coursepo'n `the"lty'pef oscillatorused. VInftlle :case'of an astable-multivihraton this wouldrbe the 'grid Vof one or bothofthe '-thes.

The operatiomof the circuit of'fig. '1"is best Lunder- Vstood withreference to 'the voltageltime digramsf Figs. 2a, 2b, and 2c. 'Inl-lig.2a, vthe. graph 50 frepre's'eh'ts the -wave form :of'anfou'tput pulse'of'the v'oscillatn g10. This Wave form lhas an initial `lvalue-e1 Tatfa time fflalnd'a Halfway up `the -A eaii- Yt2. The-.capacitor 14 shownYin dotted"lines,whieh y be the gridto`cathode=capacity of the ytube 13,*together Fig. 2b shows Athe synchronizing TUpulses ,3552.7 #Fliese'pulses will be 'seen -to have an amplitude T'greater:"tl'til the value-e3, themaximumvalue "of the wa.ve"'f50,` duration that fis `short withrespect Eto vvthat 1"of Ithe'foscillator output pulse -50.A lThree4possible positiohs .with A shown occurring atthe time t1 when the.amplitude-of Fig. 2b is a voltage-time 'graph of Ythe Vsynchronizingpulses; K

Fig. 2c is a voltage-timezgraph-.of lthe voltage appearing Aat the gridof the second cathode follower with different phase relationshipsbetween the synchronizing pulse and the leading edge .of theoutputjof'the Vcontrolled=oscilla tor; and

Fig. 2d is a voltage-time graph -of the voltageappearing across alcapacitor in the input tothe second cathode follower.

In Fig. Y1, the reference numeral .10 represents a voltage-sensitiveoscillator of one of :the :well-known types. For convenience, the outputof this 'oscillator will be, considered .to be square waves, althoughthe principle of the invention will operate just as Well withoscillators producing .other wave forms. -Theroutput of the oscillator10 appears `across a resistor 11 and is applied Ito the grid -12 of atrio'de cathode follower 13. A capacitor 14, shown in dotted lines, may'be connected between 'the grid 1f2 and the cathode '15 of thetube'13"fo"r a purthe oscillator' rpulse Eis eh a @second such'jplse{ShZb fis shown occurring'at a time t2 when Ythe!amplitude 1Ltif theoscillatorpu'lse is e2, and a third 'puls'e shown occurring at '-a 'time"t3 Whenthe amplitude "'o'f th'e :seil- Ilator pulseeisea.

In operation, assuming that 'the synchronizing pulse Voccurs rat thetime At2 -`when the oscillator wave fm Vhasfreached. the Value e2halfway to its 4 cathode `followier^13 conducts, -producing'fa Apositivpo- -tential across the 'resistor I8. The 'positive 'synchronizing pulse52h appears at the grids 23 and 41, The

diode .21 conducts, limiting Athe`p'ote`ntial at the plate 22 to theinstantaneous potential-'appearing at 'the feathode 20. This potentialis `dependent upon thef-iristantaneous value'of the wave form fr50."This willfhvefa value e2 at the time t2,a value, e1 -at anvearlierftimefil, and a value e3 .at a `latertime t3. The resultiis'pulse 53appearing at the grid 23 of the tube =24 whihfwill have the `form S3b-ifthe synchronizing-:pulse r52 occurs at time t2 when the `leading edge:51 yof the wavefon 5t) has reached the `'halfway-point. It -willhaveftheform 53a if the Vsynchronizing pulse 52 occurs at time 111 when thewave form 50 is ata `minimum value; `'.rIt

will have the form 53C the synchronizingpulseiSZ.

occurs at Vtime t3 when the wave form A-50hasi reached its maximum valuee3. AIt will--be seen-that-thislplilse' 53 has the same duration asthe-synchronizing @pulse f f Umted States Patent Ofi ice 1,58

:Tand the1 synchronizing pulse 52.

.thistime '1 resistor 35 paralleled by the diode 36, a path havingvapproximately the same impedance as the charging path but which, in theabsence of the diode 36, would be The appearance of `this positive pulse53 at the grid 23 of tube 24 tends to cause it to conduct, particularlyas tube 32 will be conducting dueto the presence of the synchronizing,pulse 52 at its grid 41.. However, the capacitor 44 assumes a chargewhenever tube 24 conducts by draw- Ying currentY from the source 16through'tube 24 and .resistor 35.k vWhen the tube 24 ceases conductingat .the end of ,the synchronizing pulse, the capacitor 44 fretains itscharge, tending to maintain the cathode at a high positive potential.This potential may be lso high that, upon the appearance of the nextpulse L53 at the grid 23 of tube 24, the cathode 30 may be too positivefor tube 24 to conduct. ycapacitor 44A discharges' through resistor 35and tube 32 which is conducting. This discharge continues until eitherthe synchronizing pulse 52 stops or the cathode i'reaches a point atwhich tube24 can conduct. This 1y 'action tends to maintain the voltageacross the capacitor f44 'at a level determined by the amplitude of thepulse 53. The diode 36 permits the potential across the cafpacitor 44 tofollow the value of the pulse 53 equally rapidly in either direction byequalizingthe impedances [of thecharging and discharging circuits. loutbefore, the charging path is through tube 24 and ,-reksistor35-which isa low resistance path. The polar- In this case,

As pointed ity of the diode 36 is such that it does not conduct at The.discharge path is through,V tube 32 and ofhigher-impedance. The voltageacross the capacitor 44 is shown* in Fig. 2d. Assuming the voltageacross capacitor 44 to be at a normal level when a synchronizing pulse52a comes through early with respect to the leading edge 51 of the waveform 50, the voltage on the cathodev 30 of the tube 24 will be too highvfor the pulse 53a .at the grid vto cause it to conduct, and tube 24will not conduct and capacitor 44 will discharge through, tube 32 from alevel e2 to a level e1, las represented by the line 54. Upon the arrivalat time t2 of a synchronizing pulse 52bcoincident with the leading edge.51 of the Wave form 50, the voltage e1 across the capaci- Vtor 44 issufficiently low to permit the tube 24 to conduct, charging thecapacitor and raising its potential along the line 55 back to the levele2. Upon the arrival at time t3 ofa synchronizing pulse 52e that trailsthe leading edge 51' of the wave form 50, the voltage e2 across thecapacitor ,44 is suciently low to permit the tube 24 to v,This-potential isl applied through the isolating cathode follower 34and over conductorr47 to the yoscillator 10 to mamtaln Vthe frequency ofthe oscillator at thedesired value.

It will be seen that the capacitor 44 acts as a memory .to maintain thepotential determined by the phase di.- Aference between the oscillatorwave form and the synchronizing pulse 53 during the interval betweensynchronizing. pulses, thus maintaining the control point of theoscillator 10 at a potential which will produce the desired'frequency. Y

. This invention is not limited to the particular details ofconstruction, materials and processes described, as many equivalentswill suggest themselves to those skilled 1n the art. It is, accordingly,desired that the appended claims .be given a broad interpretationcommensurate with the scope Vof the invention within the art.

1 fWhat is` claimed is: Y

1. In `a controlled oscillator system, a voltage-sensitive oscillator tobe controlled,means to Arectify the output of the oscillator, a'sourceof synchronizing pulses, a normally nonconducting cathode follower,.means to apply the rectified output of the oscillator to the input ofthe cathode follower, an electron discharge device having a controlgrid, said device being arranged to act as the cathode impedance of thecathode follower, meansV to couple the .synchronizing pulses to the gridof this device, and means to apply the voltage developed across thisdevice to the controlled oscillator in a manner to control its operatingfrequency. v l

2. In a controlled oscillator system, a voltage-sensitive oscillator tobe controlled producing a wave form having an appreciable rise time,means to rectify the output of the oscillator, a source of synchronizingpulses v of short duration and of an amplitude greater than the outputof the controlled oscillator, a normally non-conducting cathodefollower, means to apply the rectified output of the oscillator to theinput of the cathode follower, an electron discharge device having acontrolgrid, said device being arranged to act as the cathode impedanceof the cathode follower, means tofcouple the synchronizing pulses to thegrid of this device, and means to apply the voltage developed acrossthis device to the controlled oscillator in'a manner to control itsoperating frequency. v Y

3. In a controlled oscillator system, a voltage-sensitive oscillator tobe controlled producing a wave form having an appreciable rise time,means to rectify the output' lof kthe oscillator, a source ofsynchronizing pulses of short duration and of an amplitude greaterthan-the output of the controlled oscillator, a normally non-conductingcathode follower, means to apply-the rectified output of the oscillatorto the input of the cathode follower, an electron discharge devicehaving a control grid,said

the output of the rectifier to Vthe cathode follower, an`

electron discharge device having a Vcontrol grid, a plate and a cathode,means to utilizerthis device as ythe cathode load impedance of thecathode follower, and meansv to couple a second train of pulses tothegrid of this device to produce a voltage of an amplitude dependent onthe difference in phase between the two pulse* trains.

V5. In a phase discriminator, a rectifier, means to apr-y ply Va firsttrain of pulses having an appreciable rise kFtime to the input to therectifier, a n'ormally non-conducting cathode follower, means to applythe output of the rectier to the cathode follower, an electrondischargerdevice having a control grid, a plate and a cathode, means toutilize this device as the cathode load impedance of the cathodefollower, and means to couple a second trainl of pulses of shortduration and greater amplitude than the rst pulses to the grid of thisdevice to produce a voltage of an amplitude dependenty on the differencein phase between the two pulse trains.

6. In a phase discriminator,/a rectifier, means to ap-4 ply a firsttrain of pulses having an appreciable rise1time to the input to therectifier, a normally non-conducting cathode follower, means to applythe output of the rec-1 tier to the cathode follower, an electron'discharge device having a control grid, a plate and a cathode, means` toutilize this device as the cathode load impedance of the cathodefollower, means to couple a second train of pulsesofshort duration andgreater amplitude than the first pulses to the grid of this device, andVmeans comprisingV a capacitor shunting' the device to produce a,volt-.

age of an amplitude dependent on the difference in phase between the twopulse trains.

7. An electronic circuit comprising afree running oS illator of the typewhich is frequency sensitive to acon-` trol voltage, a pulse generatorfor providing synchronizing pulses to control the frequency and phase ofsaid oscillator, means connecting the output of said oscillator to arectifier, biasing means for normally preventing conduction through saidrectifier, said pulse generator being coupled to said rectifier to causesaid rectilier to conduct in response to said synchronizing pulses,means for impressing the output from said rectilier upon the controlgrid of a cathode follower to cause a connol voltage to lbe developedacross the cathode load of said cathode follower, and means connectedbetween said cathode load and said oscillator for applying said controlvoltage to said oscillator to control the frequency and phase of itsoscillations.

8. An electronic system comprising a free running oscillator of the typewhich is frequency sensitive to a control voltage, a pulse generator forproviding synchronizing pulses to control the frequency and phase ofsaid oscillator, a first cathode follower stage, means for mpressing theoutput of said oscillator on the input to said first stage, meansconnecting the output of said rst stage to one terminal of a rectifier,the other terminal of said rectifier being connected to a source ofbiasing potential 6 for normally preventing conduction through saidrectifier, means coupling said pulse generator to said rectifier tocause said rectifier to conduct in response to said synchronizingpulses, means for impressing the output from said rectier upon the inputof a second cathode follower stage to cause a control voltage to bedeveloped across the cathode load of said second stage, and meansconn'ected between said second stage and said oscillator for applyingsaid control voltage to said oscillator to control the frequency andphase of its oscillations.

9. An electronic system as defined in claim 8 wherein the cathode loadof said second cathode follower stage comprises a grid controllableelectron discharge device, said system further including means forimpressing said synchronizing pulses on the control grid of saiddischarge device.

References Cited in the le of this patent UNITED STATES PATENTS2,463,685 Fredendall et al. Mar. 8, 1949 2,521,058 Goldberg s Sept. 5,1950 2,717,959 Beste Sept. 13, 1955

